1. Field of the Invention
The present invention relates to an electron emission device production method for an electron emission device having an emitter electrode for field electron emission.
2. Description of the Prior Art
Recently, development of display apparatuses has been directed to make the apparatuses thinner. In such a circumstance, special attention is paid to a so-called field emission type display (hereinafter, referred to as FED) constituted by electron emission devices.
In an FED, for each pixel, there is provided an electron emission device in combination with an anode electrode and a fluorescent body arranged to opposite to this electron emission device. A plurality of such pixels are formed in a matrix to constitute a display. In this FED, an electron emitted from the electron emission device is accelerated by an electric field between the electron emission device and the anode electrode so as to strike the fluorescent body. Thus, in the FED, the fluorescent body is excited to emit light to display an image.
In general, the electron emission apparatus is a spindt type electrom emission device. As shown in FIG. 1 the spindt type electron emission device includes; a cathode electrode 100, a gate electrode 102 layered on an insulation layer 101 on the cathode electrode 100, and an emitter electrode 104 having an approximately concial shape formed in an opening 103 formed in the insulation layer 101 and the gate electrode 102 so as to expose the cathode electrode 100. In this electron emission apparatus, the emitter electrode 104 is formed so that its vertex matches with the center line of the opening 103. In the FED, a plurality of the spindt type electron emission devices are arranged corresponding to respective pixels.
In the electron emission device having such configuration, a positive potential is applied to the gate electrode 102, whereas a negative potential is applied to the cathode electrode 100, so as to generate an electric field between the gate electrode 102 and the cathode electrode 100. This electric field is applied to the tip end of the emitter electrode 104, so that an electron is emitted from the tip end of the emitter electrode 104. As has been described above, this causes the fluorescent body to emit light.
When producing such an electron emission device, firstly, the cathode electrode 100 is formed on a substrate, and then the gate electrode 102 is formed over the insulation layer 101 on the cathode electrode 100. The aforementioned opening 103 is formed by way of photo-lithographic technique.
This opening 103 is, for example, formed as follows. A mask layer having a plurality of openings is formed on the gate electrode 102. Etching is carried out on the mask layer together with the gate electrode 102 exposed by these openings, so that the openings are transferred to the gate electrode 102 and the insulation layer 101. Thus, by transferring the openings formed on the mask layer, it is possible to form an opening 103 communicating with the gate electrode 102 and the insulation layer 101.
After this, a conductive material is sputtered from various directions onto the gate electrode 102, so as to form the conical emitter electrode 104 inside the opening 103. Then, the conductive material sputtered onto the gate electrode 102 is removed, thus obtaining the aforementioned spindt type electron emission device.
In such a spindt type electron emission device, it is possible to effectively emit electrons by concentrating an electric field to the tip end of the emitter electrode 104. In other words, in the spindt type electron emission device, in order improve the electron emission characteristic, it is necessary to concentrate the electric field at the tip end of the emitter electrode 104. This is achieved by reducing the dimension of the opening formed in the gate electrode 102.
However, in the FED using the spindt type electron emission device, it is generally impossible to obtain a uniform electron emission characteristic between pixels. Because the luminance varies depending on respective pisels, it is difficult to display a clear image. Accordingly, in the FED using the spindt type electron emission device, in order to obtain a preferable image, it is necessary to take additional care to provide a uniform electron emission characteristic over the entire screen. This result can be obtained by uniformly forming the openings of the electron emission device constituting the pixels and by assuring to a strictly conical shape for the emitter electrode 104.
In the production method of the aforementioned spindt type electron emission device, when forming the opening 103 in the gate electrode 102 and the insulation layer 101, a photo-resist is used as the sacrifice layer. In this case, the photo-resist is partially exposed to light so as to form the opening in the sacrifice layer.
In this method, however, there is an optical limit in the diameter of the opening that can be formed on the photo-resist. That is, the possible diameter is on the order of 0.2 to 0.3 micrometers. Because of this limit of the dimension of the opening 103 formed in the gate electrode 102, this method cannot produce an electron emission device having a sufficient electron emission characteristic. If the dimension of the opening 103 is too large and the electron emission characteristic is insufficient, it is necessary to apply a great voltage to the gate electrode 102.
Moreover, U.S. Pat. No. 5,564,959 discloses a method for reducing the dimension of the opening formed in the mask layer. That is, an organic high molecule is used for the mask layer, to which accelerated particles such as ions are radiated so as to form a circular opening with a predetermined density. This method enables the formation of an opening having a diameter of 0.2 micrometers or less;
However, this method cannot form an opening at a predetermined position. In other words the positional accuracy of the opening is extremely low. That is, in this method, two or more openings may be overlapped. In such a case, it is difficult to uniformly form the emitter electrode. According to the method disclosed in this U.S. Pat. No. 5,564,959 it is difficult to produce an electron emission device having a uniform electron emission characteristic over a wide area.
Furthermore, PCT International Publication WO96/06443 discloses another method for reducing the dimension of the opening formed in the mask layer. That is, an insulator having a porous structure is used as the insulation layer, and an emitter electrode is formed within the porous structure of this insulation layer. A gate electrode is then formed on the porous insulation layer. By this method, it is possible to form an opening having a dimension of 0.2 micrometers or less.
In this method, however, the gate electrode is formed by deposition on the porous insulation layer and there is a chance that the conductive material constituting the gate electrode will adhere inside this porous structure. In this case, the electron emission device causes a short-circuit between the conductive material and the emitter electrode. Moreover, the wall of the porous structure may be subjected to etching so as to remove the conductive material adhered to the porous structure. However, it is difficult to completely removed the conductive material by this method to prevent the aforementioned short-circuit.